Generally, pigments coated onto an exterior material include low and high refractive index layers formed on a transparent matrix.
Typically, the low refractive index layer consists of SiO2.
Here, when the low refractive index layer is excessively thin, the pigment exhibits low brightness and low gloss. Thus, to improve brightness and gloss, a low refractive index SiO2 layer must have a large thickness. However, increase in thickness of the low refractive index layer causes a high likelihood of cracking, and results in realization of only a single color.